Hard Aluminums

[osus02]

I was curious to find a Hard, Weldable, Machinable Aluminum. I am looking at AL-6019 and AL-6020. I can not find much information on either. Does anyone know anything about these or good sites with information them relative to each other? Also any other suggestions on possible other Aluminums to use. Thanks

 

[Goahead]

Machinability should not be an issue.
Weldability is limited to resistance welding in solution and precipitation hardened alloys. 6xxx series can be heat treated after fusion welding. For hardened surfaces consider Hard Anodizing.

http://www.welding-advisers.com/

 

[swall]

What do you mean by "hard"? Aluminum is much softer than most steels. About 130 Brinell, as would be found with 7075-T6, is about as hard as the standard alloys get. This is only about Rb 80 and most steels, except the low carbon grades will exceed this. What are you trying to do, anyway?

 

[osus02]

Currently I am using a 6061-T6 Aluminum and it is being machined out and threaded. The aluminum is then being welded and after welding the threads become vary soft so soft that the valve that goes in the threads is ripping the threads out upon eventual replacement of the valve. So I need an aluminum that can be welded but stil hold strength. Obviously something allready heat treated but also in the 6xxx series. 7xxx is not an option and neither is steel.

 

[btrueblood]

Bake the part after welding in a 350 F oven for 6-8 hours. This will get you to an overaged condition.

 

[unclesyd]

What type threads does this valve have, NPT?

 

[osus02]

Yes (unclesyd) NPT. The valve itself is brass. FYI

 

[RikuY]

Try using an anti-seize lubricant on the threads. You may be experiencing some compromise if you are removing and reinstalling the threaded valves.

 

[osus02]

Thanks RikuY I have used a lubricant on the threads, but I do not like it because it is more of a band aid then it is a solution. I would prefer finding a harder Aluminum 6xxx.

 

[aviat]

I think you use a helicoil or other type of thread insert. Threading directly into Al can give lots of problems especially when it comes to removing it. As said in other posts the metal will be softer in welded area.

 

[osus02]

Thanks for the suggestion, but once again I can fix the problem once it occurs I just need to prevent it. Aren't helicoils mostly used for after the threads are ripped out? Thanks for the idea though. I would prefer finding a harder Aluminum in the 6xxx range.

 

[AlfaTony]

http://www.espimetals.com/tech/aluminum6061-t651.pdf

check this out...

Tony

 

[AlfaTony]

http://www.owenind.com/docs/12ALUMIN.pdf

and this...
Tony

 

[NickE]

osustudent02- you are repeating this statement: " I would prefer finding a harder Aluminum in the 6xxx range."

6061-T6 is one of the hardest aluminium alloys. my metals reference gives 500kg-10mm brinell hardness at 95.

There are a few other 6xxx series alloys with higher hardnesses given: 6066 6070 6262. All of these in the T9 temper will have a hardness of ~120 HB500... The problem is that this hardness is developed by cold work after the aging treatment. By welding you would remove the increased strength and hardness imparted by cold working and aging.

Helicoils are often used to strengthen threads in soft materials. Drill and tap to the helicoil 1 size larger than your thread, then insert the helicoil (I like to use red locktite to assure the helicoil attaches to the base matl') then you will have a harder thread.

You have also been given many suggestions for other ways that your problem might be solved. There isn't much else we can do for you.

Summary: 6xxx alloys are not going to solve your problem.

 

[osus02]

AlfaTony Thanks for those sites. They look pretty helpful. NickE do u know anything of Al 6019 or 6011. The Zinc enrichment in these two Aluminums leads me to believe they will be fairly hard as in 120 HB500 or even harder. I am having trouble finding resources on these two specific Aluminums. If anyone knows about them, that would be most helpful. I understand that the welding is my problem and that the material is essentially depleted of any strength gained by the temperament and heat treatment. If I am able to find a hard aluminum that has been heat-treated and can sustain some if not most of the hardness after welding that would be great. 6061-T6 is very hard I understand that as well, but through my experiments its hardness drops like a brick after welding. 6019 however only droped a little after welding. I am curious to know if anyone knows why this may have happened. What I have read makes me think it is probably the Zinc.....any ideas?

 

[CoryPad]

Alloy 6013 was developed for higher strength and improved weldability vs. other 6XXX alloys. Here is some more information:

http://www.alcoa.com/industrial/en/...d=32&market_cat_id=534&cat_id=260&prod_id=604

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[unclesyd]

I been checking on a component we made for year where a brass valve was screwed in to AL as in your case.
Pipe threads, especially small sizes, are especially prone to pullout. In our case was a worst case as we heated the part to about 280-290?F and thermal expansion, softer material, and repeated assembly all contributed to loss of integrity.
We worked on the problem from several different angles.
First we used a brass reducing bushing that was special made with male straight threads and female NPT to get a better area ratio with the AL. Redesign of the component part reduced our ability to use this bushing, size. After several iterations we end up with a brass insert for metals with internal straight pipe threads with a valve. We used valve with straight pipe threads on AL side and tubing fitting on the other side. We used several different pipe dopes, the best white lead they took away. They are using Teflon paste now.

I think the best approach is the insert route if you have the material thickness and to get away from the NPT threaded valve end if possible.

 

[osus02]

Thanks Cory and unclesyd, once again more useful information. Thanks for your time this site has proven to have a wealth of information.

 

[metman]

osustudent02,
The obvious answer to your problem has been stated twice before. Helicoils. Yes this is used commonly as a repair procedure but it is also used commonly by OEM's by original design. It is a common solution in the aircraft industry where LOTS of aluminum is used but where a screw or bolt needs to be routinely removed and replaced in the threaded hole.

Give us one good reason why not to use a helicoil. BTW I am fairly certain that Helicoil is a trade name but I do not know the generic term. Yesterday I was in a Fastenal store and they have threaded inserts by another name.

 

[btrueblood]

Two good reasons: (1) they don't make helicoils with NPT pipe threads. (2) Helicoils are not a leak tight thread.

Unclesyd's suggestion of a brass adapter is a good one - I would add the following to his suggestion: make the i.d. thread fit your NPT valve, the o.d. thread should be chosen from whatever size SAE J1926 O-ring boss seal thread that will fit, with preference given to larger sizes (larger thread diameter and more surface area will give lower stresses). Pipe dope on straight threads may seal for awhile, but with any amount of flex or thermal cycling, the joint may/will develop a leak.

OSU, do you not have access to a large enough oven to re-HT your alum. part?